Hydrometallurgy of zinc.



0. BEST.

HYDROMETALLURGY OF zmc. APPLICATION FILED MAR. 26. 1913.

1,15% 602n Patentedsept. 28, 1915.

Ore Crusher Roasfer 505 Acid Chamber Weak Solufion Tan k [I Residue Crusher I MnO Precipii'a'fed.

Wa+er PrecipH'aHng Barrel For Copper, ei'c- Precipif'aie Coppeqefc- Sforage Tank for Sh-ong Soluwion Wql'er D isploci n9 4 Tank Mixer for ComminuHn-g FilvenCake Weak A ifo'l'in Tanks Eleci'rol fe 5 9 1 Acid Neuiralized Cell H Sump Sirong Elecfrol 're 35 "acid (in slight excess) of-such strength that.

Zorro BEST, or san Emme CALIFORNIA:

' nvnnoitnrntnuney or ZINC. 1 '1 Toall whomiitmag concern:

Be it known that I',,OT'ro BEs'r, a citizen of the United States, residing at, San Frangis county of F ancisco, State of 5 California, have. invented :certain new and ."useful Improvements in Hydrometallurgy skilled in the art to which it "of Zinc; and I do hereby declare the following to-be a full, "clear, and exact description of'the invention, such as will-enable others make and use the same.- y,

My invention has for its object the'-,recov cry of zinc, on a-commercia'l scale, from zinc 3 ores and other zinc products, by a procedure which involves the obtaining'of a suitable" electrolyte inwhich the zinc is held in solu-" tion and from which it is precipitated in. a-

' non-spongy condition capable of being readily re-melted and of high purity.

In the practice of my invention I obtain the primary solution by lixiviating the zinc-- containing material by means of sulfuric acid. If the zinc-containing material is not soluble in the leaching solution, I first render it soluble in any suitable manner; as,

for instance,- in the case of zinc blende, ,by' subjecting it to. an oxidizing roast, prefer ably a sulfatizing roast, resulting inthe' formation of sulfatexof zinc with some zinc oxid. If the zinc-containing material isjal'- .i ready in'the condition of an'oxid, or if it is present as a carbonate,'the roasting operation is'omitted, as unnecessary; In any case,

however, the soluble zinc ore or zinc-conta1n1ng,mater1al 1s hxiviated by sulfuric the specific gravity of the resulting zinc sulfate solution is from 1.2 to 1.4,-,preferably 1.3. 'Heat hastens. the desired-reaction and may be obtained either by lixiviating the roasted ore while it-is still hot from the heat of roasting, or by making available the heat of solutionof anhydrous zinc sulfate, or by solution thus obtained by the lixiviation of, the zinc-containing material constitutes themaking available the heat of reaction be tween the -zinc oxid andthe sulfuric acid,

or any .or all of them, just asneeded.- The ;rous state, some alumina, silicic acid, man-- ganese, copper,,cadmium, bismuth and arsenic, wherever those elements are resent in the material to be lixiviated. By restricting appertains to" 1 zinc originally present inthe lixiviated ma' C One way of temperature, and by limiting the amount of sulfuric acid in excess to a point, where the zinc extraction is practically complete, I find" that I am able to reduce to a reasonable minimum the extraction of the impurities referred to. It-will be understood,-therefore, that, under these conditions, .the primary solution contains, practically all of the terial, and a relatively small amount of the 1 extracted impurities.

In accordance with my invention, I now precipitate out of the primary solution, certain of the impurities contained therein, by means of lime, and without precipitating out the zinc. The primary solution may, if desired, be filtered out before the addition of the li ne; but.I find that it is preferable to treat. the primary solution with the lime bethe further conduct of the operation, is ma-.

terially facilitated,- -particularly for the reason, that thelime'precipitates the soluble silicic acid present, which otherwise renders the filtration difiicu'lt It will be particularly noted that the treatment of the primary solution with lime hasfor its purpose (in addition to facilitating filtration) the removal of certain impurities, such as alumina, arsenic and the like, without precipitating any of the zinc as hereinafter (except possibly temporarily) I Specification of Letters Patent. Patented. Sept. 28, 1915. 7 Application filed' llarch 26,fl19l3. Seria1No.756,998.'

fore filtration, for the reason that, by so 7 noted, and with the precipltation of only" smallamounts of the copper present. In

fact, if the lime should temporarily precipiftate a portion of the zinc as zinc hydroxid,

the zinc hydroxidthus precipitated would 1 either react directly with the ferric or alumina-sulfate present, thereby again going'into solution as zinc sulfate,'and precipitating out a portion of the 1ron or alunnna in the form of a .hydroxid, or would be otherwise taken up by the concentrated zinc sulfate solution. a

using the lime tor advantage is as follows:

oughly stirring, slowly and gradually," a fine spray of finely divided .lime suspended n water. Only so much lime is added as is necessary to precipitate the impurities ac- To the treated ore, with the residue in suspension, I add, while thorcordin to well known equations, of which I The aluminum salts react in the same manner. Arsenic and silicic acid present ,combine'with the ferric and aluminum hydrates and form insoluble compounds. The lime Will precipitate temporarily Zn also; but the latter will react on the impurlties present, the same as Ca(OH) The following equation will serve as an example of such reaction: I r

2( O4)3+ )'2 N I i )3+ .n During all of this time, air-is beingpassed through the solution to oxidize the iron.

While the iron is not completely precipitated by the action of the lime alone, as the iron in solution is mostly present in the ferrous state, and while it cannot be completely precipitated by oxidation with air alone in a. slightly acid or neutral solution, yet it will quickly and quantitatively precipitate, if-air' is passed through the solution containing a small excess of lime or calcium carbonate. For this reason, a smallexcess of lime or calcium carbonate is employed, and oxidation, and therefore precipitation. of the iron is completed within from 15 to minutes: At the same time, as hereinbefore noted, aluminafarsenic and other impurities are. precipitated by the lime: h If ordinary slake'dlime' (milk of lime) 1s used, in the treatment described, a good many impurities are removed, some of them quantitatively. The employment of milk of lime, however, has some disadvantages, inasmuch as more or less water is thereby introduced into the solution, diluting. the zinc sulfate, and amore or less lumpy precipitate is formed, in the concentrated zinc sulfate solution, causing a loss of zinc as hydrate. Furthermore, the precipitate is rather voluminous, while the filter cake is relatively thick, and cracks easily, making washing diflicult and thereby limiting the 0 capacity and kind of ap aratus used for fil tration. I prefer, there ore, instead of using milk of lime for this purification, the use of burnt unslaked lime, and to grind it to a fineness of 100 mesh, 'or preferably 200 mesh and to then mix the same with an excess ofwater,say about two parts by weight of Water to one part of ground unslakedlime. This I call' drowning the fate solution, and immediately after drown-.

ing I may add it to the impure solution. v This ground unslaked lime, when properly prepared by mixingit quickly and thoroughly with water, does not generate much cerned. That is to say, I remove iron,.

alumina, silicia acid, quantitatively, arsenic and some other impurities almost entirely, and I have the additional advantage of less dilution of the zinc sulfate with practically no lumps, and, therefore, no loss of zinc hydroxid. I also obtain a less voluminous precipitate, which filters considerably better and forms a filter-press cake that is thinner.

and'more granular, and will not crack, and

for this reason can easily andcompletely' be- Washed free from the soluble salts, such as zinc sulfate, and other metallic sulfates. Hydrated lime acts similarly and I wish it to be understood that myinvention includes the use of both hydrated and u'nhydrated lime; After thelime treatment, the mixture is, filtered, preferably, in a continuous filter.

The filtration is fast, and the undiluted filtrate,'having a specific gravity of from 1.2 to 1.4 is kept separate from the washings, Which latter are effected With comparatively small quantities of Water. The washings (with the addition of sulfuric acid) are used for the lixiviation of subsequent ore charges,

- thusutilizing this weakjliquor without diluting the primary solution. We now have in solution the zinc as sulfate, and most of the copper, cadmium, some manganese, and also some salts of the alkalis and alkalineearths. The next step in the process" is the treatment of the above solution (of' a specific gravity of 1.2 to 1.4) with calcium permanganate, or other alkaline permanganate, in the presence of lime or calcium carbonate or other bases.

As" manganese salts-are very objectionable in the electrolytic precipitation of zinc,

causing very considerable disturbances, particularly attacking soft lead anodes, it is very essential to the attainment of the best results, that every trade of manganese'salts be removed from the solution, before it enters the electrolytic cell. I accordingly add to the zinc sulfate solution suflicient lime or calcium carbonate toneutralize the free sulfuric acid formed, when the manganese salts present are acted upon "by the permanganate, as per the. following equations, occurring simultaneously do so While subjecting the solution to vigor o ls agitation, (but' not with air, as this will I there is no high concentration of either the ZnSO, or of the lime, or of both and particularly because the lime is not added to a strong zinc sulfate solution in a heavy stream or vice versa.

In concentrated zinc sulfate solution, the

A lime is immediately surrounded by an'insolublefilmof Zn(OH )-|CaSO 2H,O, which mechanically. surrounds the lime and prevents further action on the zinc sulfate solution andvice versa. Too muchdilution of the solutions and the lime would .call for the use of apparatus of too large a size. I there. fore only dilute with the amount offweak zinc sulfate solution obtained.as wash water tion and the lime. on the opposite sides of from gypsum and displacement water, obtained from the zinc hydroxid gypsum mixture, and I prevent lumping as follows: I first place in a large, tank of say 10,000 gallons having a powerful agitatonaquantity of weak ZnSO solution. I then run .in simultaneously the strong zinc sulfate soluthe tank in suchproportions that at no time,

' I is either the zinc sulfate or thelime in large the top of opposite side of the vessel.

prefer to have always a small excess of zinc excess.'* The strong zinc sulfate solution is preferably run in close to the bottom of the vessel by means of a pump or otherwise, and

lime-in a finely divided state is run in IOIIII sulfate. Under these conditions, neither strong zinc-sulfate nor strong lime'can ever be present. The lime I use preferably is burnt, ground, unslaked lime, suspended in from 2 to 3 parts of water, which lime forms less lumps than ordinary milk of lime, besides the other-advantages enumerated above.

.As afurther precaution, I add the lime in a finely divided stream, by means of a spray nozzle or other means operating underpressure. Under these conditions, I get a precipitate free of lumps, devoid of free lime v able, and whose water is easily displaceable particles, capable of ready filtration, washby electrolyte liquor.

The zinc hydroxid or other water-insoluble zinc compound is now filtered and washed,1to remove all soluble salts, parficu- T larly soluble chlorids, that corrode soft lead anodes. It is a particular advantage of this rocess thatsoluble salts cannot accumulate, ut can be removed through this step, when- 65 ever desired and thus forming a-practically chemically pure zinchydroxid zinc carbonate, or the like, mixed with gypsum, if lime has been used as a precipitant. The gypsum does not affect the electrolysis, whether it is in solution or in suspension.

The water-insoluble zinc compound, as, for instance, zinc hydroxid gypsum mixture is now ready to be introduced into the electrolytic cycle. I have found, however; that it cannot 'be introduced into the electrolytic cycle in this form without causing 7 disturbances and without interfering with the ideal conditions of constancy aimed at in the electrolytic cycle. In the first place, the very voluminous precipitate contains a considerable amountof water, which would dilute the electrolyte when the acid solution from the-cell is run over this zinc hydroxid to neutralize the free sulfuric acid produced in said solution. Furthermore,

cfrom a practical standpoint, theprecipitated zinc hydroxid or other insoluble zinc compound should have as little bulk as possible, and should be capable of easy filtration, and the water contained in it should be capable of displacement by zinc sulfate solution of a strength equal to or greater than that of the electrolyte. Furthermore, this displacement should be possible with a minimum-ofsolution, and the zinc hydroxid should be read ily soluble in weak acids. 50 also, the remaining gypsum (in case of lime treatment) should settle fairly quickly and completely wise, the heavy residue (gypsum) should filter easily, so that zinc sulfate can be completely washed out therefrom with a minimum of water, forming a small amount of weak zinc sulfate solution, whose zinc is subsequently precipitated again as z inc hydroxid. i 7 I In order to obtain a less voluminous zinc hydroxid and one whichis ,better adapted for filtration, I either pass through the precipitate suspended in Water, carbon dioxid (washed fuel gas) or gas from the lime kiln to form basic zinc carbonate, for which purpose only a small amount of carbon dioxid is necessary, (it being desirable to stop before the solution thickens), or I use for; the

.precipitation either finely divided unslaked lime or hydrated lime as hereinbefore described for the purification of impure sulfate solution and with like resultant advantages. Furthermore, magnesium oxid in a finely divided state, say after passing through a sieve of 100 mesh, (or better 200 mesh) gives a very desirable precipitate which can easily be washed and whose water is readily displaced by electrolyte. The precipitate, thus prepared, is now in the right condition, after the displacement of ;the water by the electrolyte or zinc sulfate solution, to be introduced into the electrolyte in the strong zinc sulfate solution. Likecycle. This replacement or displacement of chlorid, according to theacetic acid, or the hydrochloric acid, as the case may be, willact merely as a carrier of 'water contained in the precipitate avoids the expense of evaporation and keeps the electrolyte of practically a constant spec fic gravity. I have now availablfor use in the electrolytic cell' a solution obtained as herei-nbefore described which,.by reason of the treatment described is a solution of practically pure zinc salt. This'solution maybe;

electrolyzed as such. If, however, I wish to use in the electrolytic cell some other Z1116 salt, as, for instance, ZlIlC acetate, I add to I the zinc jsulfate solution; an equivalent amount of calcium acetate. The. result ng reaction is as follows:

Zn 0 11 0 oaso Or, if I wish touse zinc chlorid in the. electrolytic cell, I add to the zinc sulfate- In either case, I wash out the soluble zinc.

acetate or the soluble zinc chlorid froin the insoluble gypsum and evaporate, if neces sary, to the density desired in the cell. Or I may precipitate the weak solution as zinc. hydrate, use the strong solution only. When not require replenishing, inasmuch as the zinc, with little'me'chanical'loss. From the foregoing, it will be seen that I may use'in the electrolytic cycle another acid than the one used for extraction. In fact,-'

. any acidmay be used that has a soluble lime salt, and that may be neutralized in 'a dilute.

state by zinc hydroxid or other water-insoluble zinc compound soluble in weak acid'or acids. Naturally, I can charge the electro lytic cell with any suitablezinc salt from monosul follows 5 z imso'n elect'rolyzed, gives any other source, inasmuch as it will require but very slight replenishment after it has been once charged.

- In using in thejcell bi-sulfite of zincas the i-soluble electrolyte and a water-insoluble zinc com ound, easily soluble-in weak acid,

(1 of zinc, the reactions would be as 1 no free'oxygenbeingproduced.

I In either case, the; gypsum ,formedis removed by filtration or settling; Finally,

the cellis thus charged with the-solution of zinc acetate, zinc chlorid, or the like, it does furous zinc compound .(zinc monosulfite)" into solution as zinc bisulfite,. to be returned to the acid, bringing. the water-insoluble electrolytic cell, The other molecule of sulwould react, with free sulfuric acid (as long as free'sulfuric acidis present) in accordance'with the. following equation:

If'zinc sulfate be used, it is used with a density of approximately 1.2 to 1.4, preferably about 1.27 tq 1.30. This is the density of highest electric conductivity for zinc sulfate and therefore requires a current of the least voltage with the best watt yield. Also soft lead anode corrosion is less, than in weaker solution. The zinc sulfate solution is obtained-directly of this strength, without sulfate solution is constantly needed. for dis- I placement of water in zinc hydrate or zinc hydrate gypsum mixture.

v By means of the electrolysis, pure Zinc. is deposited on the cathode and sulfuric acid is formed at the anode. The best watt yield is with an acidity betw'een0% and 3% sulfuric acid. The-excess of free sulfuric acid is neutralized by mixing it with zinc hydroxid, saturated with strong zinc sulfate solution (as hereinbefore described) and is returned to the cell as zin sulfate, withlittle or no sulfuric acid and of the same strength in, zinc sulfate. The neutralization can be effected continuously, or by runnin the acid electrolyte into a tank, adding su cient of thezinc hydroxid'gypsum mixture to make it neutralor almost neutral, allowing the gypsum now free of zinc hydroxid, -to settle,

(preferably in a continuous settler and concentrator), and returning the practically clear, neutral or slightly acid zine sulfate to the cell. The heavy residue of pure, precipitated gypsum, containing electrolyteliquor is filtered and washed (for instance, by means of a continuous filter) and can be disposed ofas an available product, for many industries; while weak solution (wash water) is treated with lime as hereinbefore described, and the precipitate is used over again after displacement 'of the water with strong zinc sulfate solution. By means of this precipitation of the wash water, evaporation is avoided. If, for any reason, the

\ electrolyte becomes impure, either because of impurities in the lime, or otherwise, it is replaced by pure zinc sulfate solution, while the impure electrolyte removed ispurified as described.

The cathodes may made of zinc, as for' instance, thin rolled'sheets of 'zinc of it inch or? inch in thickness, or even less, may' be. used. These sheets may be rolled from pure electrolytic zinc, and the sectors, including the original sheets, together with the zinc deposited thereon by the electrolysis of the solution can be shipped to the point of des tallic layer or. layers thus applied'is intended to remain on the iron cathodes during continued use, but may have to be replaced from time to time. In order that the layer or layers of .zinc'deposited from the electrolytic cell upon the coated cathodes may readily come off andseparate therefrom. I paint the coated cathodes with a solution of strong zinc sulfate and zinc hydroxid or zinc oxid (basic zinc sulfate solution), or a very concentrated zlnc sulfate solution (preferably hot) with zinc hydroxidor oxid in suspension. By this expedient, the subsequentclayers of zinc deposited on the coated cathodes can be separated-readily, no matter what metal is used for the cathode. Precipltating a coat of metallic copper or zinc on the iron cathode allowsme to use rough, unfinished plates, which make a much less expensive cathode. Near the center of the cathode, where no zinc or other metal is deposited by the current, it is best to paint the cathode with an acid-proof paint, or-

protect it-with some other acid-proof covering, as otherwise the disk would be attacked by the free sulfuric acid,'and the electrolyte would also soon" be" contaminated with iron or other salts. j 1

The anodes are ence of chlorids, manganese salts, and other impurities, and it is a particular "merit of my invention that because of the high purity of the zinc sulfate solution and its high concentration as obtained by this process, the softlead anodes employedare' hardly attacked, except for a thin filmof lead pcroxid at the surface, that practically repreferably: of soft lead-p They will corrode very quickly in the-pres mains for a longperiod of time, for the above reasons. I Referring generally to the entire procedure hereinbefore described, I desire to state that it is of very great importanceto the obtaining of the best results that the ores should be ground properly, before being roasted and 'lixiviated. In this connection, I may say, that I prefer to grind to apowder between the and mesh. sieve with 75 i the production of as small an' amoniit of fines as possible. It will, of course, be understood that I do not limit the grinding to, any particular degree of fineness, but I endeavor to exclude'the fines as much as so possible, particularly material passing a 200 mesh sieve. This is because the subsequent roasting of the fines'ls accompanied with the formation of -more acid-insoluble zinc compounds than are formed from the 5 coarser particles, and, furthermore, because filtration of the finesis very diflicult.

It will be understood that instead of In:-

iviating with dilute sulfuric acid, I- can lixiviate with any other suitable acid, as, for. 90

instance, hydrochloric acid, or any appropriate acid.

In the accompanying drawing, the process of the present invention is represented in diagram with respect to Iitsvarious steps or and the apparatus-in which they are prac- 3 tised. As indicated in this-diagram, the ore passes'from the. crusher to the roaster and thence to the extracting tanks, where the ore acid can be in part recovered fromthsulfur dioxid escaping from the roaster, in

suitable acid chambers, and in part from the weak solution resulting from thesubsequent washin of the filtered ore. From' the extracting tanks the ore passes tot'he filter where the residue is removed, after which the manganese dioxid is precipitated from the ore and filtered ofi'. Copper and similar constituents are next precipitated and filtered off, and the. resulting strong solution is. ready for-use in thesubsequent stages of the process.

For precipitating the zinc hydrate, lime, 11 5 from the lime crusher, is mixed with water and hydrated, and the hydrated lime is used as. desired for precipitating-the strong zinc sulfate solution; The precipitate is filtered, and the water therein displaced with the 12o strong ele'ctrolytefafter which the precipitate is maintainedin suspension and fed to the. acid neutralizing 5 tanks as desired. From the cell, the acid electrolyte passes to a sump where suspended matter, such as gypsum, is removed, after which the electrolyte passes to the acidneutrahzlng tanks where the acid is neutralized with the z1nc hydroxid precipitate. After settling to remove any suspended-matter such as gypsum,

is extracted with sulfuric acid of suitable 100 strength to give the desired solution. This which is filteredv oil, the electrolyte is re-' turned to the cell. water-displacing tank, and the wash water from the filter, are returned to the precipi- =tatingtank for recovering their zinc values.

As appears from the diagram, the neutralization and electro deposition are ef fected cyclically, by means of the freshly precipitated zinc compound, without how-,

ever diluting the electrolyte, the strength}, as,

well as the purity,- of the electrolyte being thus maintained.

. Having thus described my invention what a solution which comprises extracting the zinc with sulfuric acid, and treating the resulting solution before separation from the undissolved material with finely-divided unslaked lime in amount insufficient to precipitate the zinc; substantially as described.

3. In therecovery of zinc from ores and other materials containing the same, the method of obtaining a solution'which com-v prises roasting the material, extracting the roasted material while still hot from the roasting step with sulfuric acid of such strength as to-give a sulfate solution of a specific gravity within the range of 1.2 to

- 1.4, and treating the resulting solution before separation from the undissolved material with lime in amount insufficient to precipitate the Zinc; substantially as described.

4. In the recovery of zinc from ores and I other materials containing the same, the

method of obtaining a solution which comprises roasting the material, lixiviating it with sulfuric acid, treating the resultant product with lime before filtration, filtering out the solution, washing the residue and collecting the filtrate and washwater separately; substantially as described.

In the recovery of zinc from ores and other materials containing the same, the method of obtaining a solution which comprises roasting the material, lixiviating it with sulfuric acid, treating the resultant product with lime before filtration, filtering out the solution, and treating it with calcium permanganate in the presence of lime, so as to precipitate as dioxid any manganese present in the solution; substantially as described.

The water from the 6. In the recovery of\zinc from ores and other materials containing the same, the method of obtaining a solution which comprises roasting the material, lixiviating it with sulfuric acid, treating the resultant prodnot with lime before filtration, filtering out the solution, treating it with calcium permanganate in the presence of lime, so as toprecipitate as dioxid any manganese present in the solution, filtering the resultant solution and washing the precipitated manganese dioxidpsubstantially as described.

'7. In the recoveryof zinc from ores and other materials containing the same, the method of obtaining a solutiongwhich com- 'prises roastingthe material, lixiviating it with sulfuric acid, treating the resultant product with lime, filtering and precipitating traces of arsenic and any. copper, cadmium and other heavy'metals, that may be present, by vigorously agitating the solution with an excess of zinc; substantially as described. a

8. In the recovery of zinc from ores and other materials containing the same, themethod "of obtaining a'solution, which comprises roasting the material, lixiviating it with sulfuric acid, treating the resultant product withlime, filtering, precipitating traces of'arsenie and any copper, cadmium and 'other heavy metals, that may be present,

'by vigorously agitating the solution with an- 'excess of zinc, and decanting off the strong zinc sulfate solution with the precipitated copper, cadmium, etc., in suspension to separate it from the metallic zinc which immediately settles; substantially as described. 9. In the recovery of zinc from ores and other materials containing the same, the

method of obtaining a solution which comprises roasting the material, liXiviating. it

with'sulfuricacid,treating the resultant prodv not with lime, filtering, precipitating traces of arsenic and anycopper, cadmium, and other heavy metals, that may be present, by vigorously agitating the solution with an excess of zinc, decanting off the strong zinc sulfate I solution with the precipitated copper, cadmium, etc., in suspension, to separate it from the metallic zinc which immediately settles, filtering and washing the copper and other- -metals and formin further refining; su stantially as described.

them into anodes for" 10. In the recovery of zinc fro n ores and other materials containing, the same, the method of obtaining a solution which consistsin roasting the material, lixiviating it rwith sulfuric acid, treating the resultant product with lime, filtering, precipitating traces of arsenic and any copper, cadmium, and other heavy metals, that may be present, by vigorously agitating the solution with an excess of zinc, decanting ofi' the strong sulfate solution with the precipitated copper,

cadmium, etc, in suspension, to separate it from the metallic zinc, which immediately settles, and precipitating zinc from the solution as a water-insoluble compound; substantially as described;

a 11. In the recovery of z inc fromores and other materials containing the same, the method of obtaining a solution which consists in. roasting the material, lixiviating it With sulfuric acid, treating the resultant product with lime, filtering, precipitating traces of arsenicjand any co er, cadmium, and other heavymetals, that may be present,

by vigorously agitating the solution with an excess of zinc, decanting off the strong z'inc sulfate solution with the precipitated copper, cadmium, -etc., in suspension, to separate it from the metallic zinc, which 1m- -mediately settles, and precipitating zinc from the solution as a water-insoluble compound, washing to remove any soluble salts present, particularly chlorids and displac- 'ing thewater by strong zinc sulfate solution; substantially as described. 1

12. In the recovery of zinc from material containing the same, lixiviating the material with sulfuric acid of such a strength as to A give a zinc sulfate solution of. a specific gravity of 1.2 to 1. L" and treating the resultant solution with lime; substantially as described.

- 13. In' the recovery of zinc from materials containing the same, lixiviating the material with sulfuric acid, and precipitat ing out any manganese that is present by treating the solution with calcium perman .ganate in the presence of lime; substantially 'as described.

14. In the recovery of zinc from'material containing the same, lixiviating the material with sulfuric acid, and precipitating out any manganese that is present by treating the solution with calcium permanganate in the presence of lime and at about 70 (1; substantially as described.

15. In the recovery of zinc from materials containing the same, lixiviating the material with sulfuric acid, precipitating out any manganese present by means of calcium permanganate in the presence of lime, and precipitatmg. out traces ofarsenic and any copper, cadmium, and other heavy metals that may be present, by vigorously agitating the solution of zinc sulfate with an excess of zinc; substantially as described.

16. In the recovery of zinc from material containing the same, lixiviating the material with sulfuric acid, precipitating out its impurities, leaving a practically pure strong zinc sulfate, solution of a density within the range of 1.27 to 1.30, and precipitating out of said solution a zinc hydroxid gypsum 1 mixture by treating the same with lime;

substantially as described.

17. In the recovery of zinc from material containing the same, lixiviating the material with sulfuric acid, precipitating out its impurities, leaving a practically pure strong zinc sulfate solution of a density Within the range of 1.27 to 1.30, and precipitating out of said solution a zinc hydroxid gypsum mixture by treating the same with lime and passing carbon dioxid through the suspended precipitate, thereby forming basic zinc carbonate; substantiallyas described. I

18. In the recovery of zinc from material containing the same, lixiviating the material with sulfuric acid, precipitating out its impurities, leaving a practically pure strong zinc sulfate solution of a density within the range of 1.27 to 1.30, and precipitating out of said solution a zinc hydroxid gypsum mixture by treating the same with lime and passing carbon dioxid through the suspended precipitate, thereby forming basic zinc carbonate, the introduction of the carbon dioxid being interrupted before the product begins to thicken; substantially as described.

19. In the recovery of zinc from material containing the same, lixiviating the material with sulfuric acid, precipitating out its impurities, leaving a practically pure, strong zinc sulfate solution of a'density within the range of 1.27 to 1.30, depositing the zinc from said solution by electrolysis upon a suitable cathode and simultaneously forming free acid at the anode, and neutralizing the acid by running it over a zinc hydroxid gypsum mixture previously washed and saturated with strong zinc sulfate solution; substantially asdescribed.

20. In the'recovery of zinc from roasted zinc ore, the method of obtaining a strong zinc sulfate solution, with a relatively small amount of impurities therein, which comprises lixiviating the roasted ore while still hot with a small excess of sulfuric acid, thereby likewise effecting a saving in fuel,

inasmuch as the heat of the roasted ore is most of the other metallic impurities, but

with, little loss of copper, by treating the primary solution with lime and air; whereby, in addition to the purification, subsequent filtration is correspondingly improved, mainly through the removal of soluble "silicic acid; substantially as described.

22. In the recovery of zinc from ores and other materials in which is contained, the

- method of obtaining a less voluminous, more scribed. I

23. In the recovery of zinc from ores and other materials in which it is contained, the method of obtaining a less voluminous mor'e granular, and more readily filterable and washable precipitate, which consists in precipitating a zinc hydroxid gypsum mixture from a pure zinc sulfate solution by means of burnt unslaked .lime mixed with about twiceits weight of water; substantially as described. 24. In the recovery of zinc from ores and other materials containing the same, the

method of obtaining a primary solution,

' which comprises roasting the material, ex-

- method of obtaining a primary solution,

in amount insuflicient to precipitate tracting theroasted material while still hot fromxthe roasting step with sulfuric acid,

and treating the resulting solution. before separation of the undissolved material and with thoroughstirring air and.with. lime in a finely divided and granular condition and the'zinc; substantially as described.

25. In the recovery of zinc from oresiand other materials containing the same-,- the which comprises grinding the material with the practical avoidance of .fines, subjecting the material thus ground to a sulfatic roast,

' extracting 'the roasted ore while still hot from the roasting step with sulfuric acid in slight excess of that necessary for-"dissolv ing the zinc, and such strength as to give a sulfate solution of a specific gravity of about 1.2 to 1.4:, adding controlled amounts of granular hydrate'd'or unslaked lime and. I passing air through the mixture to'precipitate impurities and finally separating the solution from the undissolved residue.

26. In the recovery o'f zinc from material containing the same, lixiviating the material with sulfuric acid, precipitating out its impurities, leaying a practically pure, strong zinc sulfate solution of a density of about 1.2

. to 1.4,"p'recipitating the zinc from such so,

' density above indicated, depositing the zinc 'froma zinc sulfate solution of such density lution in the form of a zinc hydroxid gypsum mixture by means of lime, washing such precipitate and displacing the water therein by means of zinc sulfate solution of the by electrolysis and thereby forming free acid, and neutralizing the: acid and maintaining the desired concentration of the zinc sulfate solution by 'circulating the same through such zinc-hydroxid gypsum mixture.

I In the recovery'of zinc from materials containing the same, the process which com prises precipitating the zinc from its puri- 'fied solutions in theform of'hydroxid, washing the precipitate and displacing the water therein by a solution of a purified zinc salt suitable for electrolytic deposition offzinc therefrom, subjecting such a solution to electrolysis to deposit the zinc therefrom and thereby forming free-acid, and neutralizing the acid and maintaining the desired concentration of the solution by circulatingthe same through such zinc hydroxid precipitate.

28, In the recovery of zinc from materials containing the same, the process which comprises precipitating the zinc from its purified' solutions in the form of a zinc hydroxid- .therefrom and thereby forming free acid,

and neutralizing the acid and maintaining the desired concentration of the solution by circulating the same through such zinc hydroxid gypsum mixture. L 29. In the recovery of zinc from materials containing the same, the process which comprises electrolytically depositing the zinc from a purified zinc sulfate solution of a density of about 1.2 to 1.4, and thereby forming free acid, and neutralizing the acid and maintaining the concentration-of such solution bycirculating the same through a freshly precipitated soluble zinc salt.

. 1 30. In the recovery of zinc from materials containing thesame, the process which comprises electrolytically depositing the zinc from a purified-zinc sulfate solution of a density of about 1.2 to 1.4, and therebyforming free acid, and neutralizing the acid and containing the same, the process which comprises' electrolytically depositing the zinc from a purified zinc sulfate solution'of a density of about 1.2 to 1.4, and thereby forming free acid, and neutralizing the acid and maintaining the concentration of such solution by circulating the same through a freshlyprecipitated zinc hydroxid in which the water has been displaced by azinc sulv fate solution of suitable densitiy, 32. In the recovery of zinc om material containingthe same, the process which com-- prises *electrolytically depositing the z1nc from a purified zinc sulfate solution of a drensity-of about 12 to 1.4, and thereby form} or I freshly precipitated zinc hydroxid gypsum 5 mixture iniwhich the Water has been dis placed by a zinc sulfate solution of suitable density.

In testimony whereof Iafiizi my ture, in presence of two'witnesses.

' Witnesses:

HERBERT R. HANLEY, JAMES B. CATHCART.

signa- OTTO. BEST. I 

